Colorless single-crystal CVD diamond at rapid growth rate

ABSTRACT

The present invention relates to a method for producing colorless, single-crystal diamonds at a rapid growth rate. The method for diamond production includes controlling temperature of a growth surface of the diamond such that all temperature gradients across the growth surface of the diamond are less than about 20° C., and growing single-crystal diamond by microwave plasma chemical vapor deposition on the growth surface of a diamond at a growth temperature in a deposition chamber having an atmosphere, wherein the atmosphere comprises from about 8% to about 20% CH 4  per unit of H 2  and from about 5 to about 25% O 2  per unit of CH 4 . The method of the invention can produce diamonds larger than 10 carats. Growth rates using the method of the invention can be greater than 50 μm/hour.

This application claims priority of copending provisional ApplicationNo. 60/684,168, filed on May 25, 2005.

STATEMENT OF GOVERNMENT INTEREST

This invention was made with Government support under Grant No.EAR-0421020 awarded by the National Science Foundation. The Governmenthas certain rights in this invention.

INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC

Not applicable.

SEQUENCE LISTING

Not applicable.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method of producing a diamond. Moreparticularly, the present invention relates to a method of producing acolorless, single-crystal diamond at a rapid growth rate using MicrowavePlasma Chemical Vapor Deposition (MPCVD) within a deposition chamber.

2. Description of Related Art

Large-scale production of synthetic diamond has long been an objectiveof both research and industry. Diamond, in addition to its gemproperties, is the hardest known material, has the highest known thermalconductivity, and is transparent to a wide variety of electromagneticradiation. Therefore, it is valuable because of its wide range ofapplications in a number of industries, in addition to its value as agemstone.

For at least the last twenty years, a process of producing smallquantities of diamond by chemical vapor deposition (CVD) has beenavailable. As reported by B. V. Spitsyn et al. in “Vapor Growth ofDiamond on Diamond and Other Surfaces,” Journal of Crystal Growth, vol.52, pp. 219-226, the process involves CVD of diamond on a substrate byusing a combination of methane, or another simple hydrocarbon gas, andhydrogen gas at reduced pressures and temperatures of 800-1200° C. Theinclusion of hydrogen gas prevents the formation of graphite as thediamond nucleates and grows. Growth rates of up to 1 μm/hour have beenreported with this technique.

Subsequent work, for example, that of Kamo et al. as reported in“Diamond Synthesis from Gas Phase in Microwave Plasma,” Journal ofCrystal Growth, vol. 62, pp. 642-644, demonstrated the use of MicrowavePlasma Chemical Vapor Deposition (MPCVD) to produce diamond at pressuresof 1-8 kPa at temperatures of 800-1000° C. with microwave power of300-700 W at a frequency of 2.45 GHz. A concentration of 1-3% methanegas was used in the process of Kamo et al. Maximum growth rates of 3μm/hour have been reported using this MPCVD process. In theabove-described processes, and in a number of other reported processes,the growth rates are limited to only a few micrometers per hour.

Until recently, known higher-growth rate processes have only producedpolycrystalline forms of diamond. However, new methods of improving thegrowth rates of single-crystal chemical vapor deposition (SC-CVD)diamonds have recently been reported, and these methods have opened newopportunities for the application of diamond for gems, optics, andelectronics [1,2]. Several other groups have started to grow SC-CVDdiamonds [3, 4, 5]. SC-CVD diamonds reported so far, however, arerelatively small, are discolored, and/or are flawed. Large (e.g., overthree carats, as commercially available high pressure, high temperature(HPHT) synthetic Ib yellow diamond), colorless, flawless syntheticdiamonds remain a challenge due to slow growth and other technicaldifficulties [7, 8, 9]. The color of SC-CVD diamonds in the absence ofHPHT annealing can range from light brown to dark brown, thus limitingtheir applicability as gems, in optics, in scientific research, and indiamond-based electronics [6, 7, 8]. SC-CVD diamonds have beencharacterized as type IIa, i.e., possessing less than 10 ppm nitrogen,and have coloration and other optical properties arising from variousdefects and/or impurities.

Single-crystal brown SC-CVD diamonds with 4.5 mm in thickness can beproduced at high growth rates of about 100 micrometers/hour withnitrogen added, and deposited on cut-off SC-CVD seed instead of naturalor HPHT synthetic substrates [1,2]. A diamond crystal of 10 carats isapproximately five times that of commercially available HPHT diamond andthe SC-CVD diamond reported in References [7, 8, 9, 10]. Single-crystaldiamonds with larger mass (greater than 100 carats) are needed as anvilsfor high-pressure research, and crystals with large lateral dimensions(greater than 2.5 cm) are required for applications such as laserwindows and substrates for diamond-based electronic devices. Highoptical quality (UV-visible-IR transmission) and chemical purity arerequired for all of the above applications. The large SC-CVD diamondsproduced so far present problems because of the brownish color.

Attempts have been made to add oxygen in the growth of polycrystallineCVD diamond. These effects include extending the region of diamondformation [12], reducing silicon and hydrogen impurity levels [13],preferentially etching the non-diamond carbon [11, 14], and attemptingto prevent diamond cracks due to an absence of impurities [13]. Theseattempts were directed to etching and the synthesis of polycrystallinediamonds but not to the production of SC-CVD diamond.

U.S. Pat. No. 6,858,078 to Hemley et al. is directed to an apparatus andmethod for diamond production. The disclosed apparatus and method,although pioneering as a means of rapidly producing single-crystal CVDdiamonds, can lead to the production of diamonds with a light browncolor.

Thus, there remains a need to produce large, high quality,single-crystal diamonds at a rapid growth rate and to produce themcolorless (i.e., high UV-visible-IR transmission).

SUMMARY

Accordingly, the present invention is directed to a method for producingdiamond that substantially obviates one or more of the problems due tothe limitations and disadvantages of the related art.

An object of the invention relates to a method for producing a diamondin a microwave plasma chemical vapor deposition system at a rapid growthrate.

Additional features and advantages of the invention will be set forth inthe description which follows, and will be apparent, in part, from thedescription, or may be learned by practice of the invention. Theobjectives and other advantages of the invention will be realized andattained by the structure particularly pointed out in the writtendescription and claims hereof, as well as the appended drawings.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, anembodiment of the invention includes controlling temperature of a growthsurface of the diamond such that all temperature gradients across thegrowth surface of the diamond are less than about 20° C., and growingsingle-crystal diamond by microwave plasma chemical vapor deposition onthe growth surface of a diamond at a growth temperature in a depositionchamber having an atmosphere, wherein the atmosphere comprises fromabout 8% to about 20% CH₄ per unit of H₂ and from about 5 to about 25%O₂ per unit of CH₄.

In another embodiment, the method for diamond production includescontrolling temperature of a growth surface of the diamond and growingsingle-crystal diamond by microwave plasma chemical vapor deposition onthe growth surface of a diamond at a growth temperature in a depositionchamber having an atmosphere with a pressure of about 100 to about 300torr, wherein the atmosphere comprises from about 8% to about 20% CH₄per unit of H₂ and from about 5% to about 25% O₂ per unit of CH₄.

In another embodiment of the invention, the method for diamondproduction includes controlling temperature of a growth surface of thediamond and growing single-crystal diamond by microwave plasma chemicalvapor deposition on the growth surface of a diamond at a growthtemperature from about 700° C. to about 1100° C. in a depositionchamber, wherein the atmosphere comprises from about 8% to about 20% CH₄per unit of H₂ and from about 5% to about 25% O₂ per unit of CH₄.

In another embodiment of the invention, the method for diamondproduction includes controlling temperature of a growth surface of thediamond and growing single-crystal diamond by microwave plasma chemicalvapor deposition on the growth surface of a diamond at a growthtemperature in a deposition chamber, wherein the atmosphere comprisesfrom about 8% to about 20% CH₄ per unit of H₂ and from about 5% to about25% O₂ per unit of CH₄, and wherein the growth rate is greater thanabout 50 μm/hour.

In another embodiment of the invention, the method for diamondproduction includes controlling temperature of a growth surface of thediamond and growing single-crystal diamond by microwave plasma chemicalvapor deposition on the growth surface of a diamond at a growthtemperature in a deposition chamber, wherein the atmosphere comprisesfrom about 8% to about 20% CH₄ per unit of H₂ and from about 5% to about25% O₂ per unit of CH₄, and wherein the diamond grows to be over 10carats.

In another embodiment of the invention, the method for diamondproduction includes controlling temperature of a growth surface of thediamond and growing single-crystal diamond by microwave plasma chemicalvapor deposition on the growth surface of a diamond at a growthtemperature in a deposition chamber, wherein the atmosphere comprisesfrom about 8% to about 20% CH₄ per unit of H₂ and from about 5% to about25% O₂ per unit of CH₄, and wherein the diamond produced issubstantially colorless and has a UV-VIS absorption spectrumsubstantially similar to that of a man-made HPHT type IIa diamond.

In another embodiment of the invention, the method for diamondproduction includes A method for diamond production, comprising:controlling temperature of a growth surface of the diamond such that thetemperature of the growing diamond crystals is in the range of 900-1400°C. and the diamond is mounted in a heat sink holder made of a materialthat has a high melting point and high thermal conductivity to minimizetemperature gradients across the growth surface of the diamond; andgrowing single-crystal diamond by microwave plasma chemical vapordeposition on the growth surface of a diamond in a deposition chamberhaving an atmosphere, wherein the atmosphere comprises from about 8% toabout 20% CH₄ per unit of H₂ and from about 5 to about 25% O₂ per unitof CH₄.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention.

FIG. 1 is a diagram of a diamond production apparatus according to anembodiment of the present invention in which a cross-section ofdeposition apparatus with a specimen holder assembly for holding thediamond stationary during a diamond growth process is depicted.

FIG. 2 a is a perspective view of the deposition apparatus shown in FIG.1.

FIG. 2 b is a perspective view of the diamond and sheath shown in FIG.1.

FIG. 3 is a diagram of a diamond production apparatus according to anembodiment of the present invention in which a cross-section of adeposition apparatus with a specimen holder assembly for moving thediamond during the diamond growth process is depicted.

FIGS. 4 a-4 c depict cross-sectional views of holders or thermal massesthat can be used in accordance with the present invention.

FIG. 5 is a diagram of a diamond production apparatus according toanother embodiment of the present invention in which a cross-section ofa deposition apparatus with a specimen holder assembly for moving thediamond during the diamond growth process is depicted.

FIG. 6 is a flow diagram illustrating a process 600 in accordance withembodiments of the present invention that can be used with the specimenholder assembly shown in FIG. 1.

FIG. 7 is a flow diagram illustrating a process 700 in accordance withembodiments of the present invention that can be used with the specimenholder assembly shown in FIG. 3 or with the specimen holder assemblyshown in FIG. 5.

FIG. 8 is a UV-VIS spectrum for an HPHT IIa diamond; an SC-CVD diamondproduced according to the method of the invention, e.g., with adeposition chamber atmosphere comprising from about 5% to about 25% O₂per unit of CH₄; and an SC-CVD diamond produced with N₂ gas present as acomponent of the deposition chamber atmosphere.

FIG. 9 is photograph of a substantially colorless SC-CVD crystal grownaccording to the method of the invention, e.g., with a depositionchamber atmosphere comprising from about 5% to about 25% O₂ per unit ofCH₄, and an SC-CVD crystal grown with N₂ gas present as a component ofthe deposition chamber atmosphere.

FIG. 10 is an SC-CVD diamond block formed by deposition on six {100}faces of an HPHT Ib substrate.

FIG. 11 is an IR absorption spectrum (2500-8000 cm⁻¹) for an SC-CVDdiamond produced according to the method of the invention, e.g., with adeposition chamber atmosphere comprising from about 5% to about 25% O₂per unit of CH₄, and an SC-CVD diamond produced with N₂ gas present as acomponent of the deposition chamber atmosphere.

DETAILED DESCRIPTION

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. FIG. 1 is a diagram of a diamond production system 100according to an embodiment of the present invention, in which adeposition apparatus 102 is depicted in cross-section. The diamondproduction system 100 includes a Microwave Plasma Chemical VaporDeposition (MPCVD) system 104 that contains a deposition apparatus 102as well as reactant and plasma controls 106. For example, the MPCVDsystem 104 can be a SEKI AX6550 made by Seki Technotron Corp. Tokyo,Japan. This system is capable of producing 6 kilowatts of power outputat a frequency of 2.45 GHz. As another example, the MPCVD system 104 canbe a SEKI AX5250 made by Seki Technotron Corp. This system is capable ofproducing 5 kilowatts of power output at a frequency of 2.45 GHz. Asanother example, the MPCVD system 104 can be a WAVEMAT MPDR 330 313 EHPmade by Wavemat, Inc. Such a MPCVD system is capable of producing a6-kilowatt power output at a frequency of 2.45 GHz, and has a chambervolume of approximately 5,000 cubic centimeters. However, the MPCVDsystem specifications can vary with the scale of a deposition process interms of size of the deposition area and/or rate of deposition.

The MPCVD system 104 includes a chamber within the deposition apparatus102 that is at least in part defined by a bell jar 108, which is used insealing the chamber. Prior to MPCVD operations, the air within thechamber is withdrawn. For example, a first mechanical type of vacuumpump is used to draw down the chamber and then a second high vacuum typeof vacuum pump, such as a turbopump or cryopump, further draws out theair inside the chamber. Plasma is generated within the chamber by a setof plasma electrodes spaced apart within the chamber. Neither the pumpsnor the plasma electrodes are illustrated in FIG. 1.

The deposition apparatus 102 also includes a specimen holder assembly120 installed within the chamber of the MPCVD system 104. Typically, aspecimen holder assembly is positioned in the center of the depositionchamber floor 122 of the deposition apparatus 102, as shown in FIG. 1.The specimen holder assembly 120 shown in FIG. 1 is illustrated incross-section. The specimen holder assembly 120 can include a stage 124installed in the floor of the deposition apparatus 102.

As shown in FIG. 1, the stage 120 can be attached to the depositionchamber floor 122 using bolts 126 a and 126 c. The stage 124 can bemolybdenum or any other type of material having a high thermalconductivity. In addition, the stage 124 can be cooled during theprocess of growing diamond by a coolant passing through a coolant pipe128 within the stage 124. The coolant can be water, a refrigerant orother types of fluid with sufficient heat carrying capacity to cool thestage. Although the coolant pipe is shown as having a U-shaped paththrough the stage 124 in FIG. 1, the coolant pipe 128 can have ahelically shaped path or other types of paths within the stage 124 tomore efficiently cool the stage 124.

Positioned on the stage 124 of the specimen holder assembly 120, asshown in FIG. 1, is a set ring 130 having set screws, such as screws 131a and 131 c, for tightening collets 132 a and 132 b around a sheath 134that holds diamond 136. The sheath 134 is a holder, which makes athermal contact with a side surface of the diamond 136 adjacent to anedge of a top surface of the diamond 136. Because collets 132 a and 132b are tightened onto the sheath 134 by screws 131, the sheath 134 holdsthe diamond 136 in a stationary position and acts as a heat-sink toprevent the formation of twins or polycrystalline diamond along theedges of the growth surface of the diamond 136.

The diamond 136 can include a diamond seed portion 138 and a growndiamond portion 140. The diamond seed portion 138 can be a manufactureddiamond or a natural diamond. In one embodiment, the seed is a member ofa group consisting of a natural, colorless Ia diamond; a colorless IIadiamond; an HPHT synthetic yellow Ib diamond; and an SC-CVD diamond. Inanother embodiment, the seed is an SC-CVD diamond. In anotherembodiment, the seed is an SC-CVD diamond that has {100} faces. Inanother embodiment, the seed is an SC-CVD diamond that has six {100}faces. In another embodiment, all top {100} surfaces of the seed haveareas from about 1 to about 100 mm².

As shown in FIG. 1, the top surface or growth surface of the diamond 136is positioned within a region of the plasma 141 having a resonant powerat a height H above the deposition chamber floor 122. The resonant powercan be the maximum resonant power within the plasma 141 or a degreethereof. The top surface or growth surface of the diamond 136 isinitially the diamond seed portion 138 and is then the grown diamondportion 140 as the diamond grows.

As shown in FIG. 1, the top edge of the sheath 134 is at a distance Djust below the top surface or top edges of the diamond 136. The distanceD should be sufficiently large enough to expose the edges of the growthsurface of the diamond 136 to the plasma 141. However, the distance Dcan not be so large as to prevent the heat-sinking effect of the sheath134 that prevents the formation of twins or polycrystalline diamondalong the edges of the growth surface of the diamond 136. Thus, D shouldbe within a specified distance range, such as 0-1.5 mm. The distance Dand the height H, as shown in FIG. 1, are manually set using the screws131 of the set ring 130 by positioning the diamond 136 in the sheath,positioning the sheath in the collets 132 a and 132 b, and thentightening the screws 131.

FIG. 2 is a perspective view of the deposition apparatus shown inFIG. 1. In the center of the deposition chamber floor 122 of FIG. 2 is acircular stage 124 with a central recess 125. As shown in FIG. 2, thestage 124 is held in position by bolts 126 a-126 d. The stage 124 can beformed of molybdenum or other materials having a high thermalconductivity. A set ring 130 with four screws 131 a-131 b is positionedwithin the recess 125 of the stage 124 along with collets 132 a-132 b.In the alternative, the set ring 130 can be bolted to the stage 124 toincrease thermal conductance between the stage and the set ring.

As shown in FIG. 2 a, a rectangular sheath 134, which can either be ashort length of rectangular tubing or a sheet folded into a rectangle,is positioned in the collets 132 a and 132 b with a diamond 136 therein.The sheath 124 can be molybdenum or any other type of material having ahigh thermal conductivity. The screws 131 a-131 d are tightened on thecollets 132 a-132 b such that the sheath 134 is tightened onto thediamond 136 such that the sheath 134 acts as a heat sink on the fourside surfaces of the diamond 136. As shown in FIG. 1, the sheath 134also makes thermal contact to the stage 124. The collets 132 a-132 bmake thermal contact with the stage 124 and serve as thermal masses fortransferring heat from the sheath 134 into the stage 124. The tighteningof the sheath 134 onto the diamond 136 increases the quality of thethermal contact between the diamond and the sheath. As shown in FIG. 1,the sheath 134 can also make thermal contact to the stage 124. Althougha rectangular shape is shown in FIG. 2 a for both the sheath and thediamond, the sheath and the diamond can have any geometric shape such aselliptical, circular or polygonal. The shape of the sheath or holdershould be substantially the same as the diamond.

In the exemplary embodiment of the invention shown in FIGS. 1 and 2 a,the stage 124 can have a diameter of approximately 10.1 cm. and thesheath 134 can be approximately 2.5 cm wide. Regardless of thedimensions selected for the stage and the sheath 134, the thermal massof the stage 122, molybdenum sheath 124, and collets 132 can be adjustedto provide an optimal heat sink for the diamond 136. Additionally, thepath and extent of the coolant pipes 128 can be modified for greatercooling effect, especially if a particularly large diamond is to beproduced. Further, a refrigerant or other low temperature fluids can beused as a coolant.

Molybdenum is only one potential material used in the stage 124, setring 130, collets 132, sheath 134 and other components. Molybdenum issuitable for these components because it has a high melting point, whichis 2617° C., and a high thermal conductivity. In addition, a largegraphite build-up does not tend to form on molybdenum. Other materials,such as molybdenum-tungsten alloys or engineered ceramics, having highmelting points above the process temperature and a thermal conductivitycomparable to that of molybdenum, can alternatively be used instead ofmolybdenum.

Returning to FIG. 1, another component of the diamond production system100 is an noncontact measurement device, such as an infrared pyrometer142, which is used to monitor the temperature of the diamond seed 138and later the grown diamond 140 during the growth process withoutcontacting the diamond 136. The infrared pyrometer 142 can be, forexample, a MMRON M77/78 two color infrared pyrometer from MikronInstruments, Inc. of Oakland, N.J. The infrared pyrometer 142 is focusedon the diamond seed 138 or later on the grown diamond 140 with a targetarea measure of 2 mm. By using the infrared pyrometer 142, thetemperature of the growth surface of the diamond 136 is measured towithin 1° C.

The diamond production system 100 of FIG. 1 also includes an MPCVDprocess controller 144. The MPCVD process controller 144 is typicallyprovided as a component of the MPCVD system 104. As is well-known in theart, the MPCVD process controller 144 exercises feedback control over anumber of MPCVD parameters, including, but not limited to, the processtemperature, gas mass flow, plasma parameters, and reactant flow ratesby using the reactant and plasma controls 106. The MPCVD processcontroller 144 operates in cooperation with a main process controller146. The main process controller 146 takes input from the MPCVDcontroller 144, the infrared pyrometer 142, and from other measuringdevices of other components in the diamond production system 100 andcarries out executive-level control over the process. For example, themain process controller 146 can measure and control coolant temperaturesand/or flow rates of the coolant in the stage using a coolant controller148.

The main process controller 146 can be a general purpose computer, aspecial purpose computing system, such as an ASIC, or any other knowntype of computing system for controlling MPCVD processes. Depending onthe type of main process controller 146, the MPCVD process controller144 can be integrated into the main process controller so as toconsolidate the functions of the two components. For example, the mainprocess controller 146 can be a general purpose computer equipped withthe LabVIEW programming language from National Instruments, Inc. ofAustin, Tex. and the LabVIEW program such that the general purposecomputer is equipped to control, record, and report all of the processparameters.

The main process controller 146 in FIG. 1 controls the temperatures ofthe growth surface such that all the temperature gradients across thegrowth surface of the diamond are less than or equal to 20° C. Precisecontrol over growth surface temperatures and growth surface temperaturegradients prevents the formation of polycrystalline diamond or twinssuch that a large single-crystal diamond can be grown. The ability tocontrol all of the temperature gradients across the growth surface ofthe diamond 136 is influenced by several factors, including the heatsinking capability of the stage 124, the positioning of the top surfaceof the diamond in the plasma 141, the uniformity of the plasma 141 thatthe growth surface of the diamond is subjected to, the quality ofthermal transfer from edges of the diamond via the holder or sheath 134to the stage 124, the controllability of the microwave power, coolantflow rate, coolant temperature, gas flow rates, reactant flow rate andthe detection capabilities of the infrared pyrometer 142. Based upontemperature measurements from the pyrometer 142, the main processcontroller 146 controls the temperature of the growth surface such thatall temperature gradients across the growth surface are less than 20° C.by adjusting at least one of microwave power to the plasma 141, thecoolant flow rate, coolant temperature, gas flow rates and reactant flowrate.

FIG. 2 b is a perspective view of the diamond 136 shown in FIG. 1depicting exemplary points P1, P2, P3 and P4 along the growth surface137 of the diamond 136. FIG. 2 b also depicts the distance D between thegrowth surface 137 or top edges 139 of the diamond 136 and an edge 135of the sheath 134. Typically, large temperature variations, in terms oftemperature differences across the growth surface, occur between theedges and the middle of the growth surface of the diamond. For example,larger temperature gradients occur between the points P1 and P2 thanoccur between the points P1 and P3. In another example, largertemperature gradients occur between the points P4 and P2 than occurbetween the points P4 and P3. Thus, controlling temperature of thegrowth surface of the diamond such that all temperature gradients acrossthe growth surface are less than 20° C. should at least take intoaccount a temperature measurement between the middle and an edge 139 ofthe growth surface 137. For example, the main controller 146 may controlthe temperature of the growth surface such that the temperature gradientbetween points P1 and P2 is less than 20° C.

The spot size of the infrared pyrometer can affect the ability tomonitor temperature gradients across the top surface of the diamond andthus the growth rate of the diamond. For example, if the size of thediamond is large in comparison to the spot size of the infraredpyrometer, the temperature at each of the edges of the growth surface ofthe diamond can be outside of the field of view of the infraredpyrometer. Thus, multiple infrared pyrometers should be used for adiamond with a large growing area. Each of the multiple pyrometersshould be focused on different edges about the surface of the diamondand preferably near the corners, if any. Thus, the main processcontroller 146, as shown in FIG. 1, should be programmed to integrateoverlapping fields of view from the multiple pyrometers to produce acontiguous “map” of the temperatures across the diamond's surface orinterpolate between non-overlapping fields of view to a produce aninterpreted “map” of the temperatures across the diamond's growthsurface. In the alternative, the temperature gradient between a singleedge or corner point with respect to the middle of the growth surfacecan be monitored as indicative of the maximum temperature gradient thatexists across the growth surface of the diamond.

In addition to the infrared pyrometer 142 for temperature control, otherprocess control instrumentation may be included in the diamondproduction system 100. Additional process control instrumentation caninclude equipment for determining the type and quality of the diamond136 while the growth process is underway. Examples of such equipmentinclude visible, infrared, and Raman spectrometers, which are optical innature and can be focused on the same point as the infrared pyrometer142 to obtain data on the structure and quality of the diamond whilegrowth is underway. If additional equipment is provided, it can beconnected to the main process controller 146 such that the main processcontroller 146 controls the instrumentation and presents the results ofthe analytical methods along with other status information. Additionalprocess control instrumentation may be particularly useful inexperimental settings, in “scaling up” a process to produce largerdiamonds, and in quality control efforts for an existing diamondproduction system 100 and corresponding process.

As the diamond 136 grows, both the distance D and the height H increase.As the distance D increases, the heat-sinking capacity of the sheath 134for the top edges 139 of the growth surface of the diamond 136 reduces.In addition, characteristics of the plasma, such as temperature and/orconsistency, change as the growth surface of the diamond 136 extendsinto the plasma 141. In the diamond production system 100, the growthprocess is periodically halted so that the position of the diamond 136can be adjusted downward with respect to the sheath 134 to reduce thedistance D, and both the diamond 136 and the sheath 134 can be adjusteddownward with respect to the deposition chamber floor 122 to reduce theheight H. This repositioning allows the diamond growth on the growthsurface of the diamond 136 to occur within a desired region of resonantpower within the plasma 141, allows the infrared pyrometer 142 and anyadditional instruments to remain focused on the growth surface of thediamond 136, and has the effect of maintaining an efficient thermalcontact for sinking heat from the edges of the growth surface of thediamond 136. However, repeatedly halting the growth process can beinconvenient for large-scale production, and increases the chance ofintroducing contamination into the process if not carefully performed.

FIG. 3 is a diagram of a diamond production apparatus 300 according toan embodiment of the present invention in which a cross-section ofdeposition apparatus 304 with a specimen holder assembly 320 for movingthe diamond 136 during the diamond growth process is depicted. Some ofthe components of diamond production apparatus 300 are substantially thesame as those of diamond production system 100, and thus the discussionabove with regard to FIG. 1 will suffice to describe those componentslikewise numbered in FIG. 3. For example, the pyrometer 142, depositionchamber floor 122, coolant pipe 128 and bell jar 108 in FIG. 3 aresubstantially the same as those described in FIG. 1.

As shown in FIG. 3, the diamond 136 is mounted on a diamond actuatormember 360 within the sheath 134 of the specimen holder assembly 320.The diamond 136 is slidably mounted within the sheath 134 on a diamondactuator member 360 that translates along an axis substantiallyperpendicular to the growth surface. The diamond actuator member 360protrudes through a stage 324 and is controlled from underneath thestage 324 with a diamond control, which is shown as a part of thecoolant and diamond/holder controls 329 in FIG. 3. The diamond actuatormember 360 is for setting the height H between the growth surface of thediamond 136 and the deposition chamber floor 122. Although the diamondactuator member 360 in FIG. 3 is shown as a threaded rod, the diamondactuator member can be of any geometric shape that enables positioningof the diamond 136 at height or position above the deposition chamberfloor. Those skilled in the art will realize that components placedwithin the bell jar, such as the diamond actuator member 360, should bevacuum compatible so as to avoid problems in maintaining the desiredatmosphere.

The actuator (not shown) for the diamond actuator member 360 is a motor(not shown). However, the actuator can be any one of a number of knowntypes of actuator, depending on the size of diamond that is to be grown,the growth rate, and the level of movement precision required. Forexample, if the diamond 136 is small in size, a piezoelectric actuatormay be used. If the diamond 136 is relatively large or can be grownrelatively large, a motorized computer-controllable actuator ispreferred. Regardless of the particular actuator employed, the mainprocess controller 346 controls the movement of the diamond actuatormember 360 so that the diamond 136 can be automatically moved downwardas diamond growth progresses.

In addition, a holder actuator member 362 protrudes through the stage324 and is controlled from underneath the stage 324 with holder control,which is shown as a part of the coolant and diamond/holder controls 329in FIG. 3. The holder actuator member 362 translates along an axissubstantially perpendicular to the growth surface and is for maintainingthe distance D between an edge of the growth surface of the diamond 136and a top edge of the holder or sheath 134. A diamond production systemcan have a diamond actuator member, a holder actuator member, or acombination of both.

The holder actuator member 362 in FIG. 3 is threaded into the stage 324and the diamond actuator member 360 is threaded into the holder actuatormember 362. By this arrangement, the diamond and holder controls of thecoolant and diamond/holder controls 329 shown in FIG. 3 can move thediamond 136, the sheath 134, or both the sheath 134 and the diamond 136.Although the holder actuator member 362 in FIG. 3 is shown as a threadedcylinder with threading on the inside for the diamond actuator member360 and threads on the outside for threading into the stage 324, theholder actuator member can be of any geometric shape that enablesmaintaining a specified distance range between an edge of the growthsurface of the diamond 136 and the top edge of the holder or sheath 134.Those skilled in the art will realize that components placed within thebell jar, such as the holder actuator member 362 or a combination ofboth the holder actuator member and the diamond actuator member, shouldbe vacuum compatible so as to avoid problems in maintaining the desiredatmosphere.

As shown in FIG. 3, a thermal mass 364 is positioned within a recess ofthe stage 324. The holder or sheath 134 is slidably positioned withinthermal mass 364 such that thermal energy is transferred from the sheath134 to the stage 324. The top surface of the thermal mass 364 can becontoured such that heat can be transferred from the sheath 134 whileminimizing the electrical effect of the thermal mass 364 on the plasma341. Thermal masses 466 a, 466 b and 466 c in FIGS. 4 a-4 c,respectively, are examples of other contoured thermal masses withdifferent cross-sectional shapes, which in the alternative, can be usedin lieu of the thermal mass 364 shown in FIG. 3. A thermal mass can bemade of molybdenum. Other materials, such as molybdenum-tungsten alloysor engineered ceramics, having high melting points above the processtemperature and a thermal conductivity comparable to that of molybdenumcan be used as a thermal mass for transferring heat from a side of thediamond to a stage.

By minimizing the electrical effect of thermal mass 364 on the plasma341, the region within the plasma 341 in which the diamond is grown willbe more uniform. In addition, higher pressure can be used in growingdiamond, which will increase the growth rate of single-crystal diamond.For example, pressures can vary from about 100 torr to about 300 torr,and single-crystal growth rates can be from 50 to 150 microns per hour.Using a higher pressure, such as 400 torr or higher, is possible becausethe uniformity, shape and/or position of the plasma 341 are not asreadily affected by thermal mass 364, which is contoured to remove heatfrom the edges of the growth surface of the diamond and minimizes theelectrical effect of the thermal mass 364 on the plasma 341. Inaddition, less microwave power, such as 1-2 kW, is needed to maintainthe plasma 341. Otherwise, a lower pressure and/or increased microwavepower would have to be used to maintain the uniformity, shape and/orposition of the plasma 341.

As the diamond 136 grows, both the distance D and the height H increase.As the distance D increases, the heat-sinking capacity of the sheath 134for the top edges of the growth surface of the diamond 136 decreases. Inaddition, characteristics of the plasma, such as temperature, change asthe growth surface of the diamond 136 extends into the plasma 341. Inthe diamond production system 300, the growth process is halted when thediamond 136 reaches a predetermined thickness since the distance D andthe height H can be controlled by the main process controller 346, viathe coolant and diamond/holder controls 329, using the holder actuatormember 362 and diamond actuator member 360 during the diamond growingprocess. This repositioning, either manually or automatically undercontrol of the controller 144, allows the diamond growth on the growthsurface of the diamond 136 to occur within a desired region of resonantpower within the plasma 341. Further, repositioning allows the infraredpyrometer 142 and any additional instruments to remain focused on thegrowth surface of the diamond 136, and can maintain an efficient sinkingof heat from the edges of the growth surface of the diamond 136.

FIG. 5 is a diagram of a diamond production apparatus 500 according toan embodiment of the present invention in which a cross-section ofdeposition apparatus 504 with a specimen holder assembly 520 for movingthe diamond 136 during the diamond growth process is depicted. Some ofthe components of diamond production apparatus 500 are substantially thesame as those of diamond production system 100 and 300, and thus, thediscussion above with regard to FIG. 1 and FIG. 3 will suffice todescribe those components likewise numbered in FIG. 5. For example, thepyrometer 142, deposition chamber floor 122, coolant pipe 128 and belljar 108 in FIG. 5 are substantially the same as those described inFIG. 1. In another example, the coolant and diamond/holder controller329 and diamond actuator member 360 in FIG. 5 are substantially the sameas those in FIG. 3.

As shown in FIG. 5, the diamond 136 is mounted on the diamond actuatormember 360 and within a contoured thermal mass 566, which acts as aholder. By placing the diamond 136 directly within the contoured thermalmass 566, thermal efficiencies for heat-sinking the diamond 136 areincreased. However, the plasma 541 may be more easily affected since thewhole contoured thermal mass is moved by the holder actuator 562 in thestage 524 with a diamond holder control, which is shown as a part of thecoolant and diamond/holder controls 329 in FIG. 3. Thus, the mainprocess controller 546 should take into account such a factors forappropriately controlling the plasma and/or other parameters of thegrowth process. In the alternative, the convex thermal mass 364 shown inFIG. 3, the slant-sided thermal mass 466 b in FIG. 4 b, aslant-sided/cylindrical apex thermal mass 466 c in FIG. 4 c or othergeometric configurations can be used in lieu of the concave thermal mass566, in FIG. 5.

FIG. 6 is a flow diagram illustrating a process 600 in accordance withembodiments of the present invention that can be used with specimenholder assembly shown in FIG. 1. The process 600 begins with step S670in which an appropriate seed diamond or a diamond in the process ofbeing grown is positioned in a holder. In the specimen holder assembly120 of FIG. 1 for example, the diamond seed portion 138 is placed in asheath 134 and the screws 131 a-131 d are tightened by an operator.Other mechanisms can be used to maintain both the sheath and diamond inposition, such as spring loaded collets, hydraulics or other mechanismscan be used in exerting a force against the holder or sheath.

As referred to in step S672, the temperature of the growth surface ofthe diamond, either the diamond seed or grown diamond, is measured. Forexample, the pyrometer 142 in FIG. 1 takes a measurement of the growthsurface, which is the top surface of the growing diamond portion 140,and provides the measurement to the main process controller 146. Themeasurement is taken such that a thermal gradient across the growthsurface of the diamond 136 can be determined by the main processcontroller or at least the temperature of an edge of the growth surfaceof the diamond are inputted into the main process controller.

The main process controller, such as main process controller 146 shownin FIG. 1, is used in controlling the temperature of the growth surface,as referred to in S674 in FIG. 6. The main process controller controlsthe temperature by maintaining thermal gradients of less than 20° C.across the growth surface. While controlling the temperature of thegrowth surface, a determination is made to whether the diamond should berepositioned in the holder, as shown in step S675 of FIG. 6. If the maincontroller can not control the temperature of the growth surface of thediamond such that all temperature gradients across the growth surfaceare less than 20° C. by controlling the plasma, gas flows and coolantflows, then the growth process is suspended so that the diamond can berepositioned in the holder, as shown in step S678 of FIG. 6, for betterheat-sinking of the diamond and/or better positioning of the diamondwithin the plasma. If the main controller can maintain all of thethermal gradients across the growth surface of the diamond to be lessthan 20° C., then the growing of the diamond on the growth surfaceoccurs as shown in step S676 of FIG. 6.

Measuring the temperature of a growth surface of the diamond,controlling temperature of the growth surface and growing diamond on thegrowth surface occurs until it is determined that the diamond should berepositioned, as shown in FIG. 6. Although measuring, controlling,growing and the acts of determining are shown and described as steps,they are not necessarily sequential and can be concurrent with oneanother. For example, the step of growing diamond on the growth surfacecan occur while measuring the temperature of a growth surface of thediamond and controlling temperature of the growth surface are occurring.

The repositioning of the diamond, as referred to in step S678, can bedone manually or with a robotic mechanism. In addition, a determinationcan be made of whether the diamond has reached a predetermined ordesired thickness, as shown in step S673 of FIG. 6. The determinationcan be based on an actual measurement via mechanical or optical devices.In another example, the determination can be based on the length ofprocessing time in view of known growth rates for the process. If thediamond has reached the predetermined thickness, then the growingprocess is complete, as referred to by step 680 in FIG. 6. If thediamond has not reached the predetermined thickness, then the growthprocess is started again and continues with measuring the temperature ofa growth surface of the diamond, controlling temperature of the growthsurface and growing diamond on the growth surface until it is determinedthat the diamond needs to be repositioned, as shown in FIG. 6.

FIG. 7 is a flow diagram illustrating a process 700 in accordance withembodiments of the present invention that can be used with specimenholder assembly shown in FIG. 3 and FIG. 5. The process 700 begins withstep S770 in which an appropriate seed diamond, which can be a growndiamond, manufactured diamond, natural diamond or combination thereof,is positioned in a holder. In the specimen holder assembly 320 of FIG.3, for example, the diamond seed portion 138 is placed within sheath 134on the diamond actuator member 360, as shown in FIG. 3. In anotherexample of a specimen holder assembly, the diamond seed portion 138 isplaced within a contoured thermal mass 566 on the diamond actuator 360,as shown in FIG. 5.

As referred to in step S772, the temperature of the growth surface ofthe diamond, either the diamond seed or a newly grown diamond portion onthe diamond seed, is measured. For example, the pyrometer 142 in FIG. 3takes a measurement of the growth surface, which is the top surface ofthe growing diamond portion 140, and provides the measurement to themain process controller 346. In another example, the pyrometer 142 inFIG. 5 takes a measurement of the growth surface, which is the topsurface of the seed diamond portion 138, and provides the measurement tothe main process controller 546. The measurement is taken such thatthermal gradient across the growth surface of the diamond can bedetermined by the main process controller or at least the temperaturesof an edge and the middle of the growth surface are inputted into themain process controller.

A main process controller, such as main process controller 346 or 546,is used in controlling the temperature of the growth surface, asreferred to in S774 in FIG. 7. The main process controller controls thetemperature of the growth surface of the diamond such that alltemperature gradients across the growth surface are less than 20° C.While controlling the temperature of the growth surface, a determinationis made to whether the diamond needs to be repositioned in the holder,as shown in step S775 of FIG. 7. If the main controller can not maintainthe temperature of the growth surface of the diamond such that alltemperature gradients across the growth surface are less than 20° C. bycontrolling the plasma, gas flows and coolant flows, then the diamond isrepositioned while the diamond is growing as shown in FIG. 7 with the“YES” path from step S775 to both of steps S776 and S778. Byrepositioning the diamond within the holder, the heat-sinking of theedges of the growth surface is improved. In addition, the growth surfacecan be positioned within an optimal region of the plasma having aconsistency for maintaining all of the thermal gradients across thegrowth surface of the diamond to be less than 20° C. If the maincontroller can maintain all of the thermal gradients across the growthsurface of the diamond to be less than 20° C., then the growing of thediamond on the growth surface occurs without repositioning as shown inthe “NO” path from step S775 to step S776 of FIG. 7.

Measuring the temperature of a growth surface of the diamond,controlling temperature of the growth surface, growing diamond on thegrowth surface and repositioning the diamond in the holder occurs untilit is determined that the diamond has reached a predetermined thickness.As referred to in step S773 of FIG. 7, a determination is made ofwhether the diamond has reached a predetermined or desired thickness.The determination can be based on an actual measurement via mechanicalor optical devices. For example, a tracking program which records thedepth or the amount in terms of distance that the diamond had to berepositioned during the growth process. In another example, thedetermination can be based on the length of processing time in view ofknown growth rates for the growth process. If the diamond has reachedthe predetermined thickness, then the growing process is complete, asreferred to by step 780 in FIG. 7. If the diamond has not reached thepredetermined thickness, then the growth process continues withmeasuring the temperature of a growth surface of the diamond,controlling temperature of the growth surface, growing diamond on thegrowth surface and repositioning the diamond in the holder until it isdetermined that the diamond needs to be repositioned, as shown in the“NO” path from S773 to within S774 of FIG. 7.

When implementing processes 600 and 700, diamond growth is usuallycontinued as long as a “step growth” condition can be maintained. Ingeneral, the “step growth” condition refers to growth in which diamondis grown on the growth surface of the diamond 136 such that the diamond136 is smooth in nature, without isolated “outcroppings” or twins. The“step growth” condition may be verified visually. Alternatively, a lasercould be used to scan the growth surface of the diamond 136. A change inlaser reflectance would indicate the formation of “outcroppings” ortwins. Such a laser reflectance could be programmed into the mainprocess controller as a condition for stopping the growth process. Forexample, in addition to determining if the diamond is a predeterminedthickness, a determination can also be made of whether a laserreflectance is being received.

In general, the methods in accordance with exemplary embodiments of thepresent invention are designed to create large, colorless, high-qualitydiamonds with increased {100} growth rates, wherein the growth is alongthree dimensions. In one embodiment of the invention, oxygen is used inthe gas mix at a ratio of about 1-50% O₂ per unit of CH₄. In anotherembodiment of the invention, oxygen is used in the gas mix at a ratio ofabout 5-25% O₂ per unit of CH₄. Without wishing to be bound by theory,it is believed that the presence of oxygen in the gas mix of thedeposition chamber helps to reduce the incorporation of impurities inthe diamond, thus rendering the diamonds substantially colorless. Duringthe growth process, the methane concentration is in the range of about6-12%. A hydrocarbon concentration greater than about 15% may causeexcessive deposition of graphite inside the MPCVD chamber.

The process temperature may be selected from a range of about 700-1500°C., depending on the particular type of single-crystal diamond that isdesired or if oxygen is used. Polycrystalline diamond may be produced athigher temperatures, and diamond-like carbon may be produced at lowertemperatures. In one embodiment of the invention, the processtemperature may be selected from a range of about 700-1100° C. Inanother embodiment of the invention, the process temperature may beselected from a range of about 900-1100° C. During the growth process, apressure of about 100-400 torr is used. In one embodiment, a pressure ofabout 100-300 torr is used. In another embodiment, a pressure of about160-220 torr is used.

In one embodiment of the invention, the growth rate of thesingle-crystal diamond is greater than about 10 μm/hour. In anotherembodiment, the growth rate of the single-crystal diamond is greaterthan about 50 μm/hour. In another embodiment, the growth rate of thesingle-crystal diamond is greater than about 100 μm/hour.

In one embodiment of the invention, the single-crystal diamond grows tobe over 1.2 cm thick. In another embodiment of the invention, thesingle-crystal diamond grows to be over 5 carats in weight. In anotherembodiment of the invention, the single-crystal diamond grows to be over10 carats. In another embodiment of the invention, the single-crystaldiamond grows to be over 300 carats.

In one embodiment, the diamond is grown on up to six {100} faces of anSC-CVD diamond seed. In another embodiment, the diamond grown on up tosix {100} faces of the SC-CVD diamond seed is greater than about 300carats. In another embodiment, the growth of the diamond can besubstantially in two dimensions to produce a crystal of large lateraldimension (e.g., a plate of at least about one inch square) by polishingone of the longer surfaces and then growing the diamond crystal in asecond orthogonal direction on that surface. In another embodiment, thegrowth of the diamond can be in three dimensions. In another embodiment,the growth of the diamond is substantially cubic. In another embodiment,the substantially cubic diamond grown along three dimensions is at leastone inch in each dimension.

The gas mix can also include N₂. When N₂ is used, it is added to the gasmix at a ratio of about 0.2-3% N₂ per unit of CH₄. The addition of N₂ tothe gas mix at this concentration creates more available growth sites,enhances the growth rate, and promotes {100} face growth.

FIG. 8 is a UV-VIS spectrum for an HPHT IIa diamond; an SC-CVD diamondproduced according to the method of the invention, e.g., with adeposition chamber atmosphere comprising from about 5% to about 25% O₂per unit of CH₄; and an SC-CVD diamond produced with N₂ gas present as acomponent of the deposition chamber atmosphere. The SC-CVD diamondproduced with N₂ gas is light brownish in appearance and exhibited abroad band around 270 nm. This is related to the presence of non-diamondcarbon, nitrogen, and vacancies in the diamond. SC-CVD diamonds producedwith N₂ gas that have a darker brown appearance show increasedabsorption below 500 nm and a broad feature centered at 520 nm. This isnot seen in natural diamond or HPHT-grown synthetic diamond. Thebrownish color and the broad band features can be removed by HPHTtreatment, e.g., annealing. The spectrum of the diamond produced by themethods of the invention, e.g., with a deposition chamber atmospherecomprising from about 5% to about 25% O₂ per unit of CH₄, did notexhibit a broad band at 270 nm or at 520 nm, and is comparable toman-made HPHT-type IIa diamond. Without wishing to be bound by theory,applicants believe that the added oxygen reduces the hydrogen impuritylevels and the amount of non-diamond carbon.

FIG. 9 shows a colorless SC-CVD diamond produced by the method of theinvention, e.g., with a deposition chamber atmosphere comprising fromabout 5% to about 25% O₂ per unit of CH₄, on the left and a brownishSC-CVD diamond produced with a N₂, rather than O₂, in the depositionchamber on the right. Both single-crystal diamonds are approximately5×5×1 mm in size.

FIG. 10 shows an SC-CVD diamond block formed by deposition on six {100}faces of a HPHT Ib substrate, such s the 4×4×1.5 mm crystal shown below.This is an attempt to further increase the size of the diamond crystals,wherein gem-quality CVD diamond is grown according to the method of theinvention sequentially on the 6 {100} faces of the substrate. By thismethod, the three-dimensional growth of colorless, single-crystaldiamond can produce diamonds about 300 carats in weight and about 1 inchin each dimension.

FIG. 11 is an IR absorption spectrum (2500-8000 cm⁻¹) for a colorlessSC-CVD diamond produced according to the method of the invention, e.g.,with a deposition chamber atmosphere comprising from about 5% to about25% O₂ per unit of CH₄, and a brown SC-CVD diamond produced with N₂ gaspresent as a component of the deposition chamber atmosphere. Thespectrum for the brown SC-CVD diamond produced with N₂ gas had peaks at2931, 3124, 6427, 6857, 7234, and 7358 cm⁻¹. Those peaks are absent inthe spectrum for the colorless diamond produced according to the methodof the invention with O₂ gas present. The data, therefore, show thatthere are no near IR or mid IR impurities due to hydrogen in thecolorless diamond produced according to the method of the invention withO₂ gas present. This further demonstrates that the method of theinvention produces very pure, large single-crystal diamond at a highgrowth rate.

Other aspects of the invention can be understood in greater detail fromthe following examples.

Example 1

A diamond growth process was conducted in the above-described MPCVDchamber in FIG. 1. First, a commercial 3.5×3.5×1.6 mm³ high pressurehigh temperature (HPHT) synthetic type Ib diamond seed was positioned inthe deposition chamber. The diamond seed has polished, smooth surfacesthat were ultrasonically cleaned with acetone. The deposition surfacewas within two degrees of the {100} surface of the diamond seed.

Then, the deposition chamber was evacuated to a base pressure of 10-3torr. The infrared pyrometer 142 was focused though a quartz window atan incident angle of 65 degrees on the growth surface of the diamond andhad a minimum 2 mm² diameter spot size. Diamond growth was performed at160 torr pressure using gas concentrations of 15% O₂/CH₄, and 12%CH₄/H₂. The process temperature was 1020° C., and gas flow rates were500 sccm H₂, 60 sccm CH₄, and 1.8 sccm O₂. Deposition was allowed tocontinue for 12 hours.

The resulting diamond was 4.2×4.2×2.3 mm³ unpolished, and representedabout 0.7 mm of growth on the seed crystal that was grown at a growthrate 58 microns per hour. The growth morphology indicated that the <100>side growth rate was faster than the <111> corner growth rate. Thegrowth parameter, α, was estimated at 2.5-3.0.

The deposited diamond was characterized using optical microscopy, x-raydiffraction (XRD), Raman spectroscopy, and photoluminescence (PL)spectroscopy. The optical microscopy and X-ray diffraction study of theresulting diamond confirmed that it was a single-crystal.UV-visible/near infrared transmission spectra of the MPCVD grown diamondseparated from the seed diamond is distinct from MPCVD diamond grown inthe presence of N₂ gas and matches pure (Type IIa) diamond.

A number of MPCVD diamonds were produced according to the guidelines ofExample 1 while varying the described process temperature. Theseexperiments demonstrate the process temperature ranges for producingvarious types of diamond in the growth process according embodiments ofthe present invention.

The colors of diamond formed by the methods discussed above can bechanged by annealing. For example, a yellow of brown diamond can beannealed into a green diamond. Additional information with regard to thediamond produced in the examples described above is in a paper by theinventors entitled “Very High Growth Rate Chemical Vapor Deposition ofSingle-Crystal Diamond” Proceedings of the National Academy of theSciences, Oct. 1, 2002, volume 99, no. 20., pages 12523-12525, which ishereby incorporated by reference in its entirety. Diamond produced bythe above methods and apparatus will be sufficiently large, defect freeand translucent so as to be useful as, for example, windows in highpower laser or synchrotron applications, as anvils in high pressureapparatuses, as cutting instruments, as wire dies, as components forelectronics (heat sinks, substrates for electronic devices), or as gems.

As the present invention may be embodied in several forms withoutdeparting from the spirit or essential characteristics thereof, itshould also be understood that the above-described embodiments are notlimited by any of the details of the foregoing description, unlessotherwise specified, but rather should be construed broadly within itsspirit and scope as defined in the appended claims, and therefore allchanges and modifications that fall within the metes and bounds of theclaims, or equivalence of such metes and bounds are therefore intendedto be embraced by the appended claims.

REFERENCES

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1. A method for diamond production, comprising: i) controllingtemperature of a growth surface of the diamond such that all temperaturegradients across the growth surface of the diamond are less than about20° C. and ii) growing single-crystal diamond by microwave plasmachemical vapor deposition on the growth surface of a diamond at a growthtemperature in a deposition chamber having an atmosphere, wherein theatmosphere comprises from about 8% to about 20% CH₄ per unit of H₂ andfrom about 5 to about 25% O₂ per unit of CH₄, wherein the grownsingle-crystal diamond is a non-film diamond, wherein nitrogen is notadded to the deposition chamber, and wherein the diamond growth rate isgreater than about 50 μm/hour.
 2. The method of claim 1, wherein thepressure is from about 160 to about 220 torr.
 3. The method of claim 1,wherein the growth temperature is from about 700° C. to about 1100° C.4. The method of claim 1, wherein the diamond grows to be over 1.2 cmthick.
 5. The method of claim 1, wherein the diamond grows to be over 5carats.
 6. The method of claim 1, wherein the diamond grows to be over10 carats.
 7. The method of claim 1, wherein the diamond growth rate isgreater than about 100 μm/hour.
 8. The method of claim 1, wherein thegrowth of the diamond is along three dimensions.
 9. The method of claim1, wherein the diamond grows to be substantially cubic.
 10. The methodof claim 1, wherein each dimension of the substantially cubic diamond isat least one inch.
 11. The method of claim 1, wherein the diamondproduced is colorless.
 12. The method of claim 1, further comprising thestep of positioning a diamond seed in a holder.
 13. The method of claim12, further comprising the step of repositioning the diamond in theholder after the step of growing the single-crystal diamond.
 14. Themethod of claim 12, further comprising the step of repositioning thediamond in the holder while growing the single-crystal diamond.
 15. Themethod of claim 12, wherein the diamond seed is member of a groupconsisting of a natural, colorless Ia diamond; a natural, colorless Hadiamond; an HPHT synthetic yellow Ib diamond; and an SC-CVD diamond. 16.The method of claim 15, wherein the diamond seed is an SC-CVD diamond.17. The method of claim 16, wherein the SC-CVD diamond seed has {100}faces.
 18. The method of claim 17, wherein the diamond seed has six{100} faces.
 19. The method of claim 18, wherein the diamond grows to beover 300 carats.